Find the value of k for which each of the following system of equations has infinitely many solutions :
2x +3y = k
(k - 1)x + (k + 2)y = 3k
Solution
The given system of the equation may be written as
2x +3y = k = 0
(k - 1)x + (k + 2)y = 3k = 0
The system of equation is of the form
`a_1x + b_1y + c_1 = 0`
`a_2x + b_2y + c_2 = 0`
where `a_1 = 2, b_1 = 3, c_1= -k`
And `a_2 = k -1,b_2 = k + 2, c_2 = 3k`
For a unique solution, we must have
`a_1/a_2 - b_1/b_2 = c_1/c_2`
`=> 2/(k-1) = 3/(k +1) = (-k)/(-3k)`
`=> 2/(k -1) = 3/(k +1) and 3/(k +1) = (-k)/(-3k)`
`=> 2(k + 2) = 3(k - 1) and 3 xx 3 = k + 2`
`=> 2k + 4 = 3k - 3 and 9 = k + 2`
`=> 4 + 3 = 3k - 2k and 9 - 2 = k`
=> 7 = k and 7 = k
k = 7 satisfies both the conditions
Hence, the given system of equations will have infinitely many solutions if k = 7